Triphenylethylene antiestrogens are estrogen antagonists used in the treatment of hormone dependent cancers such as breast cancer. These components are mixed agonists/antagonists in many tissues and species and therefore, are useful probes in the study of how estrogens cause coordinated biological responses. Our laboratory will continue to study the interaction of the estrogen receptor bound by estrogen versus antiestrogen with nuclear acceptor sites, defined as specific chromosomal proteins in tight association with specific DNA sequences which confer high affinity and specificity to the binding of steroid receptors within nuclei. These chromosomal nonhistone proteins may be responsible for alterations in chromatin structure allowing steroid receptors to interact with necessary transcriptional components. These acceptor sites may be located in the nuclear matrix near genes that code for oncogene products which, in turn, stimulate other genes necessary for complex responses such as differentiation and growth. Some acceptor sites interact with either antiestrogen- or estrogen-receptor complexes, whereas some interact only with antiestrogen-receptor complexes or only with estrogen- receptor complexes. We will characterize the protein component of these acceptor sites. Nonhistone proteins will be purified by extraction from rabbit uterine or MCF-7 cell chromatin with high molarities of chaotropic agents, followed by molecular sieve chromatography and SDS-polyacrylamide gel electrophoresis. Acceptor activity will be determined after reconstitution to DNA by reverse gradient dialysis. We will determine the amino acid sequence of purified acceptor proteins and obtain monoclonal and polyclonal antibodies to these proteins. This will allow us to determine if acceptor proteins belong to a known class of DNA-binding proteins. We will also clone the genes for acceptor proteins which will aid us in obtaining greater quantities of these proteins for study and allow us to determine tissue and species specificity of the acceptor proteins.